The present invention relates to a process for producing thiolcarbamates which can be used as effective agricultural chemicals. More particularly, it relates to an improved process for producing thiolcarbamates by reacting carbonyl sulfide with a sec-amine and a halogenated hydrocarbon in an aqueous medium.
Heretofore, it has been known to produce thiolcarbamates by (1) a process for reacting a benzyl halide with an aqueous solution of an alkali metal salt of thiocarbamic acid in U.S. Pat. No. 3,144,475.
However, in the process, the benzyl halide which is reacted with the alkali metal salt of thiolcarbamic acid is water insoluble whereby the reaction of the benzyl halide with the aqueous solution of an alkali metal salt of thiolcarbamic acid is a heterogeneous reaction and the reaction is not smoothly performed to cause certain disadvantages of a long time for the reaction and low yield of the object product.
The following processes have been proposed as improved processes for producing thiolcarbamates to overcome the disadvantage in the process (1). (2) A process for reacting benzyl halide with the alkali metal salt of thiolcarbamic acid in a mixed solvent of water and acetone, methanol or ethanol. (Japanese Patent Publication No. 28427/1973.) (3) A process for reacting carbonyl sulfide with sec-amine in an organic solvent to produce an amine salt of thiolcarbamic acid and further reacting the product with an alkyl halide or benzyl halide. (Japanese Unexamined Patent Publication Nos. 88030/1975 and 78832/1977. ) (4) A process for reacting an alkyl halide with an aqueous solution of an alkali metal salt of thiolcarbamic acid in the presence of a catalyst of a quaternary ammonium salt, a quaternary phosphonium salt, a quaternary ammonium type resin or a quaternary phosphonium type resin. (Japanese Unexamined Patent Publication No. 108908/1977.)
That is, in the process (2), a water soluble organic solvent such as acetone, methanol and ethanol is used as the solvent for the reaction and the reaction of benzyl halide with an aqueous solution of an alkali metal salt of thiolcarbamic acid is performed in a homogenous system whereby the reaction is smoothly performed.
In the process (3), the reaction is performed by using amine salt of thiolcarbamic acid as the thiolcarbamic acid salt and using an organic solvent such as aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, N,N-lower dialkyl formamides, lower dialkyl sulfoxides, lower alkyl cyanamides, and nitrobenzenes as the solvent for reaction; to react an alkyl halide or a benzyl halide with the amine salt of thiolcarbamic acid in the organic solvent in the homogeneous system whereby the reaction is smoothly performed.
In the process (4), the reaction of an alkyl halide with an aqueous solution of an alkali metal salt of thiolcarbamic acid is smoothly performed by using a quaternary ammonium salt, a quaternary phosphonium salt a quaternary ammonium type resin or a quaternary phosphonium type resin as the catalyst.
However, in the process (2), the water soluble organic solvent such as acetone, methanol or ethanol is used whereby the contamination of the water soluble solvent into a drainage can not be prevented to cause an environmental pollution, disadvantageously.
In the process (3), the organic solvent is used whereby the recovery of the solvent is required from the viewpoints of cost and environmental safety whereby a recovery step is required disadvantageously. Moreover, in the process (4), the expensive water soluble quaternary ammonium salts, quaternary phosphonium salts, etc. are used as catalyst, whereby the contamination of the catalyst into the drainage can not be prevented to increase nitrogen content and phosphorus content in the rivers, seas or lakes and marshes and to cause the environmental pollution and it is economically disadvantageous and it requires a long reaction time, disadvantageously.
As described, the processes (2) to (4) are not suitable as the process for producing thiolcarbamates from the viewpoints of the requirements of environmental safety and non-pollution and low cost.
The inventors have studied to overcome the disadvantages by producing an aqueous solution of an amine salt of thiolcarbamic acid by reacting carbonyl sulfide with a sec-amine in an aqueous solution and then reacting a halogenated hydrocarbon with the amine salt of thiolcarbamic acid.
The inventors have found that the reaction of the amine salt of thiolcarbamic acid with the halogenated hydrocarbon is smoothly performed even though it is a heterogeneous reaction.